The dehydration of waste water slurry separated from a solid-liquid mixture by a solid sleeve centrifuge presents the problem of preventing the separated solid and liquid from remixing together in the discharge area of the centrifuge. It is desirable that such re-mixing be held to an absolute minimum so that additional treatment of the discharged solids is not necessary, and the solids may be stored or reprocessed in the state from which they are discharged from the centrifuge.
An attempted solution, as shown in the German Laid Open Specification No. 1,532,678 was to position a static plate or disc on the rotating worm in the area of transition from the cylindrical portion to the conical portion. The centrifuge was then operated in such a manner so as to maintain a relatively high liquid level in the cylindrical sleeve portion which, in combination with the static plate, prevented backflow of the precipitated solids to some degree. This solution has the disadvantage of also preventing backflow of liquid which is still mixed with the solids in the conical discharge portion of the centrifuge. Further demoisturizing of the solids in the discharge portion of the centrifuge is therefore not possible, because the liquid mixed with the solids in the discharge portion is discharged along with the solid.
In accordance with the present invention, a method and apparatus for post-dehydration of solids separated from the liquid in the cylindrical separating portion of the centrifuge consists in providing a static plate attached to the rotating worm in the transition area between the cylindrical and conical portions, and also providing liquid conducting members carried on the cylindrical portion of the worm which communicate beyond the static plate to allow additional demoisturizing of solids in the conical portion of the centrifuge.
It is thus an object of the present invention through these measures to attain a higher degree of post-dehydration of the solids in the conical sleeve portion of the centrifuge to such an extent that the discharged solids may be stored directly therefrom or may be burnt with only slight expenditure of fuel.
A further object of the invention is to minimize disturbances in the cylindrical sleeve portion of the centrifuge which may result from uncontrolled backflow of liquid from the conical to the cylindrical portion of the centrifuge.
Another object of the present invention is to improve separation of solids and liquids in a solid-liquid mixture by preventing re-mixing of liquids removed from the solid in the discharged portion of the centrifuge with liquids and solids in the separating portion of the centrifuge. Liquid flowing back from the conical portion to the cylindrical portion may vary in solid content depending upon the nature of the mixture being separated. Preventing this backflowing liquid from remixing with materials in the cylindrical separating portion of the centrifuge results in solids having a lower liquid content reaching the discharge portion of the centrifuge.
Further details, features and advantages of the invention will be apparent from the following explanation of the embodiments shown in the drawings.